This invention concerns improvements in or relating to mineral mining machines, particularly, but not exclusively, of the kind known as shearer drum cutter loaders.
Such machines are used extensively in coal mining wherein they are arranged to travel reciprocally within a seam to win coal from a longwall face. In the course of the winning operation, dust is generated by the impact of the cutting picks on the coal. It has long been the practice to utilize water sprays to suppress the dust to make the working environment more acceptable, the sprays being mounted adjacent the cutting picks which are arranged in an appropriate lacing pattern on scrolled loading vanes secured to the surface of the drum. It is also common practice to provide on the face end of the drum a clearance ring which has mounted thereon high-pressure water jets for the purpose of assisting the cutting operation itself. These particular jets reduce the cutting forces on the picks, thus allowing either faster cutting rate to be achieved or a reduction in the number of picks on the clearance ring resulting in the production of smaller amounts of fine coal.
The deployment of high-pressure water sprays in the manner described also yields a significant decrease in the amount of respirable dust produced, a reduction in pick wear and lower transient loading of the machine components caused by vibration. However, the major problem attendant upon their usage is that of supplying the water at sufficient pressure to be effective. There is normally insufficient surplus power available to drive a high-pressure pump from the shearer electric motor, and space limitations preclude the provision of an independently driven on-board pump. Equally, a pump located remotely from the shearer is impractical because of the safety problems associated with feeding high-pressure hose along the coal face.
The relatively lower pressure water sprays disposed adjacent the picks across the surface of the cutting drum for dust and frictional sparking suppression are usually supplied with water from the mine water supply, but this is normally at too high a pressure owing to the hydrostatic head caused by the depth of the mine workings. Depressurization is, therefore, necessary before feeding the water to the cutting drum.